Remove child package max.

Any value we pick now is likely not to make any sense later.  Since devices
don't have any limit on the number of installed apps, and we're talking
about priv-apps here, a limit isn't necessary.

Test: Framework tests and on Pixel device.

Change-Id: I05b1edc0e96dd8ca2a16e8a542f302efb1dcf6f8